The proposed research deals with the investigation of ocular toxoplasmosis. Specifically, it deals with the pathogenesis of the ocular lesions of this disease, with the immunologic responses of the host to Toxoplasma infection, and with the nature of the antigens that evoke those responses. It seeks to identify ways in which immunologic intervention might be implemented to the benefit of the patient with ocular toxoplasmosis. Cell-mediated immunity is recognized as an indispensable component of protection against this infection. The interaction of sensitized lymphocytes with macrophages appears to be essential to the destruction of Toxoplasma parasites in the lesion. The activities of macrophages in the ocular lesions of toxoplasmosis will be investigated at the ultrastructural level. Histochemical studies will be performed on these macrophages to discern the nature of the enzyme reactions that result in the destruction of Toxoplasma. Therapeutic studies will be performed on an animal model of ocular toxoplasmosis, and the effects of subconjunctivally administered clindamycin will be assayed in human subjects.